Such apparatuses are known, for example, in the laboratory field. Here the measurement channel is milled into a surface in an expensive manner. Cleaning of the milled notch is very expensive and complex. Furthermore, the milled passage may have only a limited cross-section. Differently dimensioned measurement channels require the use of a complete different viscometer.
DE 689 29 247 [U.S. Pat. No. 4,817,416] discloses a viscometer where the plastic melt is branched off from an extruder, guided to a measuring path driven by a pump, and pumped back into the extruder by a further pump. For this purpose the measurement channel is comprised of two blocks between which an exchangeable capillary plate is arranged. However, the measuring apparatus has a many parts and is constructed in a costly manner, and its operation is very elaborate with regard to switching the capillary plate.